Status of YeMiGO: Underground micro-gravity observatory in South Korea

We present the operational status and performance of the Yemi Micro-Gravity Observatory (YeMiGO) following the installation of the iGrav#001 superconducting gravimeter (SG) at Yemi underground laboratory (YemiLab), South Korea, in October 2022. Situated at a depth of 1,003 m below the surface (118 m below mean sea level), YeMiGO provides a unique ultra-low-noise environment for high-precision geodynamic studies.
Noise characterization using data from September 2023 demonstrates exceptional stability, particularly within the seismic frequency band, confirming the site’s suitability for high-sensitivity gravity monitoring. A calibration factor of -94.38±0.14 μGal/V was determined through a joint observation campaign with the FG5-231 absolute gravimeter.
During the initial 587-day observing run (O1), the SG successfully captured numerous seismic events, including a significant co-seismic gravity offset of 0.561 μGal triggered by a magnitude 6.2 earthquake 765 km away. Preliminary comparative analysis between the iGrav and conventional seismometers suggests that the SG exhibits a more stable response to earthquake distance, offering complementary data for broad-band seismic research.